1. Field of the Invention
Present invention relates to; a silicon-containing film used as an intermediate layer in a multi-layer resist process used in microprocessing in manufacturing of a semiconductor element and the like, especially a silicon-containing film-forming composition that is suitable to form an intermediate layer by a spin coating method; a silicon-containing film-formed substrate; and a patterning process using this.
2. Description of the Related Art
With highly integrated LSI's providing highly increased speeds, finer pattern rules are being rapidly promoted. Commensurately with the fineness, the lithography technique has attained formation of fine patterns, by virtue of light sources of shorter wavelengths and resist compositions appropriately selected therefor. The main role thereof was played by positive photoresist compositions to be each used as a monolayer. The monolayer positive photoresist composition is configured to possess, in a resist resin, a frame having an etching resistance against dry etching by chlorine-based or fluorine-based gas plasma, and to possess such a resist mechanism that an exposed area is made dissolvable, so that the exposed area is dissolved to thereby form a pattern, and the remaining resist pattern is used as an etching mask to dry etch a processing substrate coated with the resist composition.
However, when a pattern is made finer, i.e., pattern rules are further narrowed while keeping a thickness of a used photoresist film as it is, the photoresist film is deteriorated in resolution performance. Further, when the resist film is to be developed by a developer to form a pattern, a so-called aspect ratio thereof is made excessively large, thereby resultingly causing a pattern collapse. Thus, the fineness has been accompanied by decrease in photoresist film thickness.
Meanwhile, although for processing of a processing substrate, there is typically used a method for processing the processing substrate by dry etching by adopting a patterned photoresist film as an etching mask, practically no dry etching methods exist to exhibit a complete etching selectivity between a photoresist film and a processing substrate, so that the resist film is also damaged during processing of the processing substrate and the resist film is collapsed, thereby failing to accurately transfer a resist pattern onto the processing substrate. Thus, with finer patterns, resist compositions have been required to have higher dry etching resistances.
Further, since shortened wavelengths of exposure have demanded that resins having lower light absorption at exposure wavelengths are used for photoresist compositions, such resins have been subjected to a transitional history from a novolak resin, through polyhydroxystyrene, and to a resin having an aliphatic polycyclic frame, commensurately with a transitional history from i-beam, through KrF, and to ArF. However, etching speeds under the dry etching condition have been practically made higher, so that recent photoresist compositions having higher resolutions practically tend to be rather lowered in etching resistance.
This obliges a processing substrate to be dry etched by a photoresist film which is inevitably thinner and weaker in etching resistance, thereby making it urgent to ensure a material and a process in this processing state.
As one method to solve such a problem, multi-layer resist process have been used. The methods are configured to: interpose a resist intermediate film having an etching selectivity different from that of a photoresist film, i.e., a resist upper layer film, between the resist upper layer film and a processing substrate; obtain a pattern in the resist upper layer film; thereafter transfer the pattern to the resist intermediate film by dry etching by using the obtained resist upper layer film pattern as a dry etching mask; and further transfer the pattern onto the processing substrate by dry etching by using the obtained pattern of the intermediate film as a dry etching mask.
In a bilayer resist process as one of the multi-layer resist processes, a silicon-containing resin is used as a resist composition of a upper layer film, and a novolak resin is used as an intermediate film (Japanese Patent Laid-Open (kokai) No. H6-95385, for example). The silicon resin exhibits an excellent etching resistance against reactive dry etching by oxygen plasma, but is easily etched and removed by using fluorine-based gas plasma. In turn, the novolak resin is easily etched and removed by reactive dry etching by oxygen gas plasma, but exhibits an excellent etching resistance against dry etching by fluorine-based gas plasma, chlorine-based gas plasma, or the like. Thus, a novolak resin film as a resist intermediate film is formed on a processing substrate, and a resist upper layer film adopting a silicon-containing resin is formed thereon. Next, the silicon-containing resist film is subjected to pattern formation by a post treatment such as irradiation of energy beam, development, and the like, and the formed pattern is used as a dry etching mask in a manner to remove a novolak resin by reactive dry etching based on oxygen plasma at those portions of the novolak resin where the resist pattern material has been developedly removed, to thereby transfer the pattern to the novolak film. Further, the pattern transferred to the novolak film is used as a dry etching mask, thereby enabling pattern transference to the processing substrate by etching based on fluorine-based gas plasma, chlorine-based gas plasma, or the like.
Since such a pattern transference based on dry etching leads to obtainment of a transferred pattern in a relatively excellent profile when an etching resistance of the etching mask is sufficient, problems are scarcely caused such as pattern collapse due to friction or the like by a developer upon development of a resist, thereby allowing for obtainment of a pattern having a relatively large aspect ratio. Thus, even for a fine pattern which has not been directly formed due to pattern collapse upon development or the like due to a problem of aspect ratio when a resist film exemplarily adopting a novolak resin has been made to have a thickness corresponding to that of the aforementioned intermediate film, the above-described bilayer resist process allows for obtainment of such a novolak resin pattern having a sufficient thickness as a dry etching mask of a processing substrate.
The multi-layer resist process further include a three-layer resist process which can be performed by using a typical resist composition used in a monolayer resist process. For example, this method is configured to form: an organic film as a resist lower layer film based on novolak or the like on a processing substrate; a silicon-containing film as a resist intermediate film, thereon; and a typical organic photoresist film as a resist upper layer film, thereon. Since the organic resist upper layer film exhibits an excellent etching selectivity ratio relative to the silicon-containing resist intermediate film for dry etching by fluorine-based gas plasma, the resist pattern is transferred to the silicon-containing resist intermediate film by means of dry etching based on fluorine-based gas plasma. According to this method, patterns of novolak films having sufficient dry etching resistances for processing can be obtained similarly to the bilayer resist process insofar as patterns can be transferred to silicon-containing films, even by adopting: a resist composition which is difficult to be formed with a pattern having a sufficient film thickness for direct processing of a processing substrate; and a resist composition having an insufficient dry etching resistance for processing of a substrate.
Examples of silicon-containing resist intermediate films to be used in the above-described three-layer resist process include silicon-containing inorganic films by CVD, such as SiO2 films (Japanese Patent Laid-Open (kokai) No. H7-183194, for example) and SiON films (Japanese Patent Laid-Open (kokai) No. H7-181688, for example); and films obtained by spin coating, such as SOG (spin-on-glass) films (Japanese Patent Laid-Open (kokai) No. H5-291208, for example), and crosslinkable silsesquioxane films (Japanese translation of PCT international application No. 2005-520354, for example); and polysilane films (Japanese Patent Laid-Open (kokai) No, H11-60735, for example) would also be usable. Although the SiO2 films and SiON films have excellent performances as a dry etching mask upon dry etching of an underlying organic film, a specific equipment is required for film-formation. Contrary, the SOG films, crosslinkable silsesquioxane films, and polysilane films can be formed by only spin coating and heating, and are thus considered to be high in process efficiency.
The applicability of the multi-layer resist process is not restricted to an attempt to enhance a resolution limit of resist film. In a via-first method which is one of substrate processing methods where a processing intermediate substrate has large height differences, an attempt to form a pattern with a single resist film encounters a problem such as inaccurate focusing during resist exposure due to a substantial difference in resist film thickness. In such a case, the height differences are filled by a sacrificial, film and flattened thereby, then a resist film is formed thereon and a resist pattern is formed, and this situation inevitably entails usage of the aforementioned multi-layer resist process (Japanese Patent Laid-Open (kokai) No. 2004-349572, for example).
Silicon-containing films having been conventionally used in such a multi-layer resist process have several problems. For example, it is well known that when a resist pattern is intended be formed by photolithography, exposure light is reflected by a substrate and interferes with incident light, to cause a problem of so-called standing waves, and it is required to interposingly provide an antireflective film as an intermediate film so as to obtain a fine pattern which is free of edge roughness of photoresist film. Particularly, reflection control is indispensable, under the most-advanced high NA exposure conditions.
Then, it becomes necessary to interpose an organic antireflective film between a silicon-containing film and a photoresist film to be formed on the silicon-containing film, in a process for forming the silicon-containing film as a resist intermediate film, particularly by CVD in a multi-layer resist process. However, when such an organic antireflective film is to be additionally interposed, it becomes necessary to pattern the organic antireflective film by using the photoresist film as a dry etching mask, such that transference to processing of the silicon-containing film is allowed after dry etching of the organic antireflective film by using the photoresist film as the mask upon dry etching. As such, the overlying photoresist film is subjected to an additional burden of dry etching to an extent the processing of the organic antireflective film. Particularly, most-advanced photoresist films have been made small in thickness, so that such dry etching burden is not negligible. Thus, attention has been directed to a three-layer resist process utilizing a light-absorbing silicon-containing film as a resist intermediate film which is free of occurrence of the aforementioned etching burden.
As the light-absorbing silicon-containing intermediate film, a light-absorbing silicon-containing intermediate film of a spin coating type has been known. For example, a technique in which an aromatic structure is used as a light-absorbing structure is disclosed (Japanese Patent Laid-Open (kokai) No. 2005-15779, for example). However, an aromatic ring structure, which absorbs a light efficiently, has an effect to decrease a dry etching rate in dry etching process by a fluorin-based gas plasma; and thus, this technique is to a unfavorable direction in carrying out dry etching of an intermediate film without a load to a photoresist film. Accordingly, when this kind of the light-absorbing substituent group is added, an appropriate dry etching process is prioritized, and a measure is taken in a direction to lower the light-absorption efficiency by regulating amount of the light-absorbing substituent group or by decreasing thickness of the intermediate film; and thus, this leads to decrease in an antireflection function thereby adversely affecting a lithography process.
Accordingly, a material with a low load, especially to a upperlayer photoresist film in a dry etching process, while having an adequate antireflection function, has been desired.